The present invention relates to the field of photography and, more particularly, to a camera including an automatic lens focusing system.
Commonly-assigned U.S. Pat. No. 4,167,316 discloses a camera having an automatic lens focusing system that is operated in conjunction with a sonic ranging system for measuring the photographic subject-to-camera distance.
The lens focusing system includes a plurality of discrete lens elements, each having a different focal length, mounted in circumferentially spaced apart relation on a lens holding disc for rotation about a center axis to sequentially present the lens elements at a focusing position for focusing image forming light rays emanating from a subject located within a correspondidng subject-to-camera distance range at the camera's film plane.
As the sonic ranging system (which may be of the type described in commonly-assigned U.S. Pat. No. 4,199,246) operates, the disc is accelerated by the arm of a torsion spring to impart rotary motion thereto. After receipt of an echo signal from the subject indicative of subject distance, a disc pawl operates to engage a corresponding one of a plurality of notches disposed about the periphery of the disc to thereby stop disc motion and locate the lens element corresponding to the indicated distance range at the focusing position.
The disc accelerating torsion spring is mounted on a disc latch and actuator plate for pivotal motion therewith to push against a pin on the lens disc. The latch and actuator plate, in turn, is adapted to be rapidly pivoted to engage the acceleration arm of the torsion spring with the disc pin by a pivotally mounted walking beam which also serves to open and close a shutter blade mechanism for controlling exposure interval. The walking beam, in turn, is pivoted in response to the retraction of a solenoid plunger upon energization of the solenoid winding to initiate the cycle of camera operation. Thus the energy for pivoting the disc accelerating torsion spring is derived from the solenoid operating through the linkage provided by the walking beam and disc latch and actuator plate.
While this system works satisfactorily, it tends to be mechanically complex and relatively expensive because the solenoid must be carefully tested and selected to insure that it provides the right amount of energy for disc rotation in response to retraction of its plunger. Also, there will be some dissipation of energy by the operation of the walking beam and actuator plate which must be accounted for in determining the amount of energy ultimately delivered to the torsion spring for acceleration. For this system to work properly, the amount of energy delivered by the torsion spring must be in a predetermined allowable range to insure that the disc rotates at a velocity that is within allowable limits.
Commonly-assigned copending applications U.S. Ser. Nos. 17,196, now U.S. Pat. No. 4,243,309, and 17,425, now U.S. Pat. No. 4,315,676, both filed on Mar. 5, 1979, and U.S. Ser. No. 156,044 now U.S. Pat. No. 4,307,952, filed on Jun. 3, 1980, disclose a somewhat simplified system wherein disc rotation is effected by application of a force to a disc mounted tab or pin by one end of a pivoting arm that serves as a combined blade mechanism latch and lens disc actuator. The latch and actuator member is pivoted by energy provided through an actuator arm (more fully described in commonly-assigned U.S. Pat. No. 4,040,072) which derives its energy through a mechanical linkage back to a manually operated camera cycle actuator assembly. Again, the acceleration energy is applied to the disc through a rather long mechanically complex linkage therefore making it difficult and expensive to insure that the proper amount of energy is applied to the disc to effect its rotation within the allowable speed range.
Therefore, it is a primary object of the invention to provide a camera with an automatic lens focusing system wherein the source of energy for effecting rotation of the lens carrying disc is applied directly thereto rather than through a complex mechanical linkage which will necessarily dissipate some of the energy in its operation in a difficult-to-control manner.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.